1. Field of the Invention
The present invention relates to a means for improving the processing of polyolefin resins that are coupled with polar substrates via grafted polyolefins.
2. Description of Related Art
GMT (glass mat reinforced thermoplastic) is a rapidly growing area in automotive applications.
Grafted polyolefins are commonly used as coupling agents and compatibilizers between polar substrates (mineral fillers, glass, polymers) and unmodified base polyolefins. These grafted polyolefins include, inter alia, maleic anhydride and acrylic acid modified polypropylene, polyethylene, and copolymers thereof. The coupling mechanism generally includes the reaction or interaction of the grafted functionality with the polar substrate and the co-crystallization of the grafted polyolefin with the base polyolefin.
However, compounds containing such grafted polyolefins can be difficult to process owing to the increased adhesion of the composition to metal surfaces through the reaction of the maleic anhydride or acrylic acid with the adsorbed water on the metallic surface in question. For example, some glass mat thermoplastic compounds require maleated polypropylene for improved coupling of a polypropylene base resin to a sized glass fiber reinforcement. During processing, the composition can adhere to metal surfaces present in the processing equipment. As a result, a problem arises as to how to promote coupling between the grafted polyolefin and the polar substrate, while at the same time reducing the tendency for increased adhesion owing to the reaction of, for example, maleic anhydride or acrylic acid, with metallic surfaces of the processing equipment, especially the double belt press, commonly used in GMT production.
A similar problem exists where similar compositions, particularly those comprising highly filled LSOH (low smoke, zero halogen) compounds, are used in wire and cable applications, which require optimally minimized adhesion in order to provide an easier stripping jacket.
U.S. Pat. No.4,003,874 discloses that a modified polyolefin obtained by adding to 100 parts by weight of a polyolefin 0.01 to 0.8 parts by weight of an unsaturated carboxylic acid or anhydride thereof having 3 to 8 carbon atoms in the molecule and 0.05 to 0.5 part by weight of an organic peroxide and melt-mixing these components in an extruder has outstanding adhesion to glass fibers. A blend of such a modified polyolefin filled with glass reinforcements is said to have excellent physical properties, as well as excellent appearance. The modification of the polyolefin may be effected in the presence of glass reinforcement to achieve both modification and mixing in a single stage, resulting in a composition with superior physical properties owing to improved dispersion and a low level of breakdown of the glass reinforcement.
U.S. Pat. No. 4,535,113 discloses olefin polymer compositions containing silicone additives that can be extruded through relatively narrow die gaps at commercial extrusion rates to provide film material characterized by improved mechanical and optical properties.
U.S. Pat. No. 4,663,369 discloses a glass-fiber reinforced polypropylene composition said to have superior adhesion to the glass fibers therein, stiffness, high-impact properties and molding properties. The composition comprises a graft polypropylene resin obtained by graft-polymerizing a radically polymerizable unsaturated compound onto a crystalline polypropylene resin with an organic catalyst in a hydrocarbon solvent or a blend of the graft polypropylene with a crystalline polypropylene resin, glass fibers treated with an organic silane or titanium compound, calcium stearate and an alkaline earth metal compound.
U.S. Pat. No. 5,236,514 discloses a purging composition useful in cleaning and removing contaminants from processing equipment. The purging composition comprises:
(a) at least one metal adsorbate compound, PA1 (b) a matrix resin, and optionally, PA1 (c) at least one abrasive, and/or PA1 (d) a carrier resin having a melting point different from that of the matrix resin. PA1 1. 20 to 80 parts by weight of glass fibers having a length of at least 3 mm and an average diameter of 20 .mu.m or less, and PA1 2. 80 to 20 parts by weight of a crystalline propylene polymer at least partly modified with an unsaturated carboxylic acid or a derivative thereof, the MFR (melt flow rate) of the modified polymer being 50 g/10 min or more, in which the glass fibers are present in constituent 2 in such a state that they are arranged almost in parallel with one another; and
Additionally, processing aids may be present in the composition to serve as conditioning agents on the relatively clean surface generated during purging. A purging composition master batch can be made by mixing 5 percent of a weak metal adsorbate, 10 percent abrasive filler, 5 percent conditioning processing aid, such as UCARSIL PA-1 Processing Aid ( a processing agent comprising a polydimethylsiloxane with pendant polyether groups) in a resin having a higher melting point than the bulk of the resin used for purging. Suitable higher melting carrier resins include polypropylene and the like when used in polyethylene as a matrix. The resin is then extruded and pelleted. Two percent of this master batch is mixed with a purging matrix resin containing about 90 percent resin (e.g., linear low density polyethylene) and about 10 percent filler.
U.S. Pat. No. 5,308,648 discloses a process for applying a polymer additive material, which may, inter alia, be UCARSIL PA-1 Processing Aid, to a polymeric substrate, wherein the process includes the steps of (a) forming in a closed pressurized system a mixture of a solid polymer additive material, a suitable liquid carrier material, and a suitable viscosity reducing material, and (b) spraying this mixture onto a polymeric substrate.
U.S. Pat. No. 5,484,835 discloses a heat-resistant, propylene resin-based material comprising:
A. Three to 97 percent by weight of a resin-impregnated glass fiber bundle comprising: PA0 B. 97 to 3 percent by weight of a crystalline propylene polymer having an MFR of 50 g/10 min or more.
It is said that a surface treatment of the glass fibers with a silane coupling agent, for example, an epoxy-silane such as .gamma.-glycidoxypropyl trimethoxy silane, a vinyl-silane such as vinyltrichlorosilane, or an amino-silane such as .gamma.-aminopropyl triethoxysilane, can improve the heat resistance, strength and antiwarping properties of the resulting molding material.
U.S. Pat. No.5,646,207 discloses an aqueous sizing composition for glass fibers said to be particularly useful for the reinforcement of thermoplastic or thermosetting matrix polymers that contain a film-forming material, fluorescent whitening agent, coupling agent, stabilizing agent and lubricant. The film-forming material is selected to be compatible with the thermosetting or thermoplastic matrix polymer used in the ultimate forming process. The sizing compositions are said to be particularly advantageous for sizing glass fibers to be used in the reinforcement of matrix polymers for forming molded parts.
U.S. Pat. No.5,670,552 discloses a process for producing thermoplastic foam, including: (a) melting a thermoplastic polymer to produce a polymer melt; (b) introducing a carbon dioxide blowing agent into the polymer melt; (c) adding to the polymer melt one or more additives selected from the group consisting of (1) polysiloxane (which can be UCARSIL PA-1), and (2) mineral oil; and (d) extruding and foaming the melted polymer, blowing agent, and one or more additives to produce thermoplastic foam. The quality of the foams made from a carbon dioxide blowing agent is said to be substantially improved by the addition of the additives.
European Patent Application 0 421 002 A1 discloses a method and composition for lowering the oxygen permeability and enhancing the thermal stability and melt shear stability of monolayer and multilayer packaging films having a layer of vinylidene chloride copolymer film by adding an organic silicon polymer to the vinylidene chloride copolymer. The organic silicon polymer may be UCARSIL PA-1. It is said that, by virtue of the organic silicon polymer, the conventional stabilizer/plasticizer combination of epoxy resin and 2-ethylhexyl diphenyl phosphate may be eliminated from the vinylidene chloride copolymer.
European Patent Application 0 455 092 A2 discloses stable dispersions of a solid phase in a functional fluid and the addition of the stable dispersion to thermoplastic polymers. The functional fluid may be UCARSIL PA-1. It is taught that the resultant thermoplastic polymer compositions are characterized by improved properties and can be formed into products of desired configuration.
WO 95/25074 discloses an aqueous chemical treatment or size for silaceous fibers and fillers that has a polyolefin compatible film-forming polymer, an organo-functional coupling agent, and at least one stabilizer to produce a polyolefin reinforcing article.
Volk et al., The Effect of Silicone Lubricant on the Extrusion and Quality of Linear Polyethylene, Muanyag es Gumi 26(9):257-69 (1989) discloses that the addition of 5 weight percent dimethyl siloxane (UCARSIL PA-1) to a master batch containing 90% linear polyethylene and Super Floss antiadhesive agent reduces torque during extrusion, melt pressure, and the temperature of the melt. The optical properties and aesthetic value were reported to be improved also by using PA-1.
Processing aids are also known in the art as lubricants, which describes the mechanism by which they function. Silicone processing aids are used in mainly mineral filled polyolefins to reduce the friction between the melt and the extruder and between the melt and the filler particles. PA-1 is a special silicone and has proved too expensive for this application. The same effect can be achieved with cheaper silicones, stearates, and the like.
Most GMT is currently produced without a coupling agent. The main reason for this is that the coupling agent reacts with hot metal (especially the double belt press) and adheres to it. This adhesion can be very severe, causing major surface damage to the GMT sheet and considerable down time as the adhered material is manually cleaned off the belt. GMT producers would like to get the improved properties that the use of a coupling agent would provide, but this adhesion problem limits their use.
The disclosures of the foregoing are incorporated herein by reference in their entirety.